Cigarette smoking and white matter microstructure

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Abstract
Rationale Diffusion tensor imaging has been used before in testing associations between cigarette smoking and white matter integrity, with inconsistent results. Published reports indicate higher fractional anisotropy (FA, a measure of linear water diffusion) in some brain regions and lower FA in others in adult smokers compared to nonsmokers. Adolescent smokers exhibited elevated FA at several brain regions and a positive correlation of FA in the genu corpus callosum with exposure to smoking (pack-years). Objective To help resolve prior discrepancies, we studied adults, sampling multiple brain regions, and testing for relationships to clinical features of nicotine dependence and exposure to smoking. Methods Brain MRI scans (1.5 T) were acquired, and FA and apparent diffusion coefficient (ADC, a measure of random diffusion) were assayed in corpus callosum and prefrontal white matter, corona radiata, internal capsule, cingulum bundle, and hippocampal perforant fibers in 18 smokers (33.7 ± 7.9 years of age) and 18 age- and gender-matched nonsmokers. Results ADC showed no group difference, but smokers had higher (4.3–21.1%) FA than nonsmokers. The differences were significant in right prefrontal white matter, cingulum, and genu corpus callosum. FA in several regions was negatively correlated with nicotine dependence or cigarettes/day. Conclusions Combined with earlier findings, these results suggest a model of changing trajectories whereby FA is higher with tobacco exposure during adolescence and declines with continued smoking in adulthood. This notion is supported by the observation that, at multiple sampling sites, participants who had started smoking earlier in life had higher FA than those who had started later.

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